The electromagnetic device drivers of the past have not adequately solved the dual problem of low power dissipation and fast reset time. For example, in FIG. 3 of U.S. Pat. No. 3,558,997, a driver circuit is shown wherein both pick and hold currents are supplied by high power circuits connected to a high voltage power supply. Although lower power is dissipated in the coil during hold mode, high power is still dissipated in the driver circuit during hold mode because of the high voltage power supply connection. Further, there are no means provided for rapidly resetting the driver circuit to make it rapidly available for a subsequent pick and hold cycle. Additionally, the driver requires separate pick and hold signals to regulate the duration of the pick and hold intervals respectively, rather than a single actuating signal for both pick and hold.
Another prior art driver described in U.S. Pat. No. 3,582,981 utilizes the charge stored on a capacitor to provide a pick current for a short interval until the charge on the capacitor is dissipated. A smaller hold current is then supplied by a transistor. At the conclusion of an actuating cycle, the driver cannot be reactuated until a charge is again built up on the capacitor. The capacitor is connected to the power supply by a high impedance. The time to recharge the capacitor is therefore long. No means are provided for rapidly returning the capacitor to its initial charged state by rapidly recharging it, and therefore the device cycling rate is low. Further, even if the capacitor was connected to the power supply by a low impedance, to thereby increase the charging speed, the power dissipation of the driver circuit would increase dramatically, as the low impedance would draw a high current from the power supply during the pick and hold intervals.